Do transient hydrological processes explain the variability of strontium-90 activity in groundwater downstream of a radioactive trench near Chernobyl ?

Mathieu Le Coz (1) , Léa Pannecoucke (2, 3) , Albane Saintenoy (4) , Chantal de Fouquet (2) , Xavier Freulon (2) , Charlotte Cazala (1)

1 IRSN/PSE-ENV/SEDRE/LELI - Laboratoire de recherche sur le devenir des pollutions de sites radioactifs
2 GEOSCIENCES - Centre de Géosciences
3 IRSN/PSE-ENV/SEDRE - Service des déchets radioactifs et des transferts dans la géosphère
4 GEOPS - Géosciences Paris Saclay

The Chernobyl Pilot Site (CPS) was created in 2000 in order to study radionuclide migration processes to the geosphere from radioactive material of the Red forest buried in a trench. In this article, the data collected in the CPS up to 2015 are analyzed to identify the links between hydrological conditions and release of strontium-90 (90 Sr) from the trench. Then, a flow-and-transport model is used for simulating distribution of 90 Sr both in the unsaturated and saturated zones downstream of the trench. The results show that the 90 Sr activity in groundwater is strongly transient in time, due to the high inter-annual variability of both the recharge rate and the groundwater level (some particularly wet winters resulted in saturation of the bottom part of the trench). In addition, the parameters that govern the sorption of 90 Sr in trench material appear to vary significantly in space (the retardation factor ranges from 10 to 50 depending on the location). This spatiotemporal variability could hide some critical processes, e.g., related to a long-term trend, and needs to be characterized through an appropriate sampling frequency.

Mots clés: weather time-series groundwater fluctuation radioactive waste groundwater modelling variably saturated flow; weather time-series; groundwater fluctuation; radioactive waste; groundwater modelling; variably saturated flow

Domaines: Sciences de l'environnement

Mathieu Le Coz, Léa Pannecoucke, Albane Saintenoy, Chantal de Fouquet, Xavier Freulon, et al.. Do transient hydrological processes explain the variability of strontium-90 activity in groundwater downstream of a radioactive trench near Chernobyl ?. Journal of Environmental Radioactivity, 2023, 259-260, pp.107101. ⟨10.1016/j.jenvrad.2022.107101⟩. ⟨irsn-03951276⟩